21061866 has 48 divisors (see below), whose sum is σ = 49740480. Its totient is φ = 5927040.

The previous prime is 21061819. The next prime is 21061871. The reversal of 21061866 is 66816012.

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 20370 + ... + 21378.

It is an arithmetic number, because the mean of its divisors is an integer number (1036260).

Almost surely, 2^21061866 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21061866, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24870240).

21061866 is an abundant number, since it is smaller than the sum of its proper divisors (28678614).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21061866 is a wasteful number, since it uses less digits than its factorization.

21061866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1099 (or 1092 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21061866 is about 4589.3208647903. The cubic root of 21061866 is about 276.1630783771.

Adding to 21061866 its reverse (66816012), we get a palindrome (87877878).

The spelling of 21061866 in words is "twenty-one million, sixty-one thousand, eight hundred sixty-six".